Leak cited in Delta 4 Anomaly; X-37B Is Cleared To Launch

A fuel leak was behind a performance anomaly with a Delta 4 rocket (above) during its launch of an X-37B. Credit: ULA photo

WASHINGTON — United Launch Alliance (ULA) said a fuel leak was behind a performance issue with a Delta 4 rocket’s upper-stage during an Oct. 4 launch but that the hiccup should not affect similar hardware aboard the Atlas 5 rocket now being prepped to launch a U.S. Air Force space plane Dec. 11.

The launch of the X-37B space plane from Cape Canaveral Air Force Station, Fla., had been scheduled for Oct. 25 but was delayed to allow ULA and the Air Force to investigate the earlier anomaly. The space plane’s mission is classified.

The fuel leak, in the interior of the thrust chamber of the Delta 4’s Pratt & Whitney-built RL-10 engine, occurred during the successful launch of a GPS satellite from Florida. It started during the first engine start sequence of the launch, ULA said in a Dec. 7 press |release.

The Atlas 5 slated to launch the X-37B space plane, or Orbital Test Vehicle (OTV), uses a different variant of the RL-10 engine.

ULA spokeswoman Jessica Rye said company inspectors at the Cape performed extra work ahead of a Dec. 7 launch readiness review to make sure the Atlas 5 was not at risk of having the same issue.

“What we’re doing is looking at [the Atlas 5’s] upper engine, doing borescope inspections and making sure at this point about that engine, that one in particular,” Rye said. “Typically, we would not do that type of inspection, but it’s something that we can do if we want to get a better look at the engine.”

ULA said its investigation into the Oct. 4 anomaly continues. However, “all credible crossover implications from the Delta anomaly for the OTV-3 Atlas vehicle and engine system have been thoroughly addressed and mitigated, culminating in the flight clearance decision for the OTV-3 launch,” the company said.

The Boeing-built X-37B scheduled to launch Dec. 11 has flown in space once before, logging 225 days in orbit following its April 22, 2010, launch. Another X-37B returned to Earth in June after 469 days in space.

The upcoming X-37B launch would be the Air Force’s third OTV mission. OTV-3 was supposed to launch Oct. 25 but got caught up in delays as ULA and the Air Force probed the Oct. 4 Delta 4 launch anomaly.

The next spacecraft slated to fly on a Delta 4 is the Wideband Global Satcom 5, a military communications satellite that will launch from Cape Canaveral. Due to the ongoing ULA and Air Force investigations, there is no launch date for that mission, which had been scheduled for early 2013.